On the availability of wireless sensor networks

The success of wireless sensor networks relies on effective power-saving schemes. In this paper, we investigate a particular operating scheme: the sensor's communication function is alternately activated (on) and deactivated (off). The rationale of this scheme is mainly due to the facts that the communication function dominates the power consumption and, in many applications, data can be periodically transmitted to the sink. The investigation is conducted with a new metric called the availability. Since the availability at equilibrium can be readily determined by the averages of the on and off durations, rather than their intrinsic probability distribution functions, using this metric avoids the usual difficulty of estimating the distributions. Both qualitative descriptions and quantitative evaluations through several case studies are presented in this paper.